DIY Astronomy tool

This is a multipurpose tool meant to aid in the use of telescopes, it features:

• Zeroable Compass (not tilt compensated), with 0.1 degree resolution. Stores offset to EEPROM.
• Zeroable Clinometer with 0.1 degree resolution. Stores offset to EEPROM.
• Zeroable 2 axis digital Level with 0.1 degree resolution. Stores offsets to EEPROM.
• Brightness control.

These can be useful for leveling a telescope and for doing basic polar alignment, or as a very simple alt-azimuth display of telescope position.

Here is a 6 minute youtube video describing how it works:

Hardware used:

• Arduino Mega328 development board (UNO, Pro or similar). The one in the video is a Pro mini 5V 16Mhz
• HMC5883 sensor module, I used the GY-271 variant.
• MMA8452 accelerometer, I used the GY-45 variant.
• 7 Segment, 8 Digit, MAX72XX controlled, 5 Wire LED display.
• KY-040 Rotary encoder, for user input (selecting mode, zeroing the compass and inclinometer, adjusting display brightness)

Arduino pinout:

• SDA = A4 (4.7K pullup to VCC recommended)
• SCL = A5 (4.7K pullup to VCC recommended)

MMA8452 pinout:

• SDA, SCL and GND: matching the Arduino
• VCC (from Arduino) to VCC_IN, not to the 3V3 pin
• SAO (address select) to GND.
• When used as a digital level, the accelerometer is meant to be used horizontal (Z axis pointing to the sky).
• When used as inclinometer or DSC, the acelerometer is meant to be used vertical, with the Z axis pointing to the horizon.

HMC5883 (or GY271) pinout:

• SDA, SCL, VCC and GND: matching the Arduino
• DRDY pin disconnected
• The HMC5883 is meant to be used on a permanently horizontal position (not attached to the telescope tube)

MAX72XX LED Display:

• VCC and GND: matching the Arduino
• DIN (Data In) connected to Arduino pin 12
• CLK connected to Arduino pin 11
• LOAD (CS) connected to Arduino pin 10

KY-040 Rotary Encoder:

• CLK connected to Arduino pin 2
• DT connected to Arduino pin 3
• SW connected to Arduino pin 4, and through a 10K pullup to VCC.
• VCC (sometimes labeled "+") connected to Arduino VCC
• GND connected to Arduino GND